1. Field of the Invention
The present invention relates to a video processing apparatus that can be connected to a video playback apparatus, more particularly to a video processing apparatus capable of generating different interpolated frame images according to a playback mode of the video playback apparatus and performing frame rate conversion.
2. Description of the Related Art
Recently, video equipment conducts frame rate conversion to display an image at a higher frame rate in order to suppress blur and flicker of moving images.
Japanese Patent Application Laid-Open No. 2001-054066 describes an image display system that differentiates the decoding process speed of a moving image read from a digital versatile disk (DVD) media between a standard playback mode and a special playback mode. Such processing can reduce the processing amount in slow playback, and can provide a smooth display when fast-forward playback is performed.
Japanese Patent Application Laid-Open No. 03-263989 also describes a technique of obtaining a motion vector from the preceding and subsequent frames, and using the motion vector to generate interpolation data as a method for generating interpolated frames in frame rate conversion processing.
A frame rate conversion method in the conventional video processing apparatus, however, has a problem that a smooth image is not always displayed when video data is input in the special playback mode. This problem is in particular described as follows:
(1) In a Case of Fast-Forward Playback (FIG. 2)
When playback is carried out in the normal playback mode, frame images from input image data are continuously transferred into a frame rate converter as images n0, n1, and n2. On the other hand, when the fast-forward playback is carried out, the frame images from the input image data are thinned to be images n0, n10, and n20 and transferred into the frame rate converter. In this case, the frame rate converter generates an interpolated frame image n0′ from images n0 and n10, and an interpolated frame image n10′ from images n10 and n20. When an interpolated frame image is generated from a frame image temporarily separated as described above, an interpolation error can easily occur because of lower correlation between frames. When an image is generated and displayed with the interpolation error, smoothness of a moving image is impaired.
(2) In a Case of Frame-by-Frame Advance Playback (FIG. 3)
When a frame-by-frame advance playback is carried out, a frame image n0 of an input video is input to a frame rate converter until the user starts to perform the frame-by-frame advance playback. When the user starts to perform the frame-by-frame advance playback (at the time of the user action in FIG. 3), the next frame image n1 is input. The frame rate converter generates an interpolated frame image n0′ from frame images n0 and n1 at a time when the frame is changed after the user performs a playback action. Although the user wants to sequentially view each frame of the input video in frame-by-frame advance playback, the interpolated frame image 0′ that does not originally exist is displayed.
(3) In a Case of Slow Playback (FIG. 4)
When a slow playback is carried out at a half speed, the same frame is input to the frame rate converter successively twice such as n0, n0, n1, n1, and n2, n2. The frame rate converter generates an interpolated frame image n0′ from frame images n0 and n1, and an interpolated frame image n1′ from frame images n1 and n2.
Frame rate images output from the frame rate converter are images n0, n0, n0, n0′, n1, n1, n1, n1′, and n2, n2, n2. In other words, the same images alternatively appear a different number of times such as thrice (n0), once (n0′), thrice (n1), once (n1′), and thrice (n2). When times of display of the same frame are different, the motion image is displayed with poor smoothness.